1. Field of Invention
The present invention relates to a fluid droplet discharge device such as a printer that has a vacuum platen that pulls recording paper to a platen surface that determines the printing position, and relates more particularly to an improved suction hole and the surface configuration of the vacuum platen.
2. Description of Related Art
Holding the recording paper tight to the platen surface that defines the printing position and maintaining a precise platen gap is important in order to ensure print quality in an inkjet printer, which discharges ink droplets to print on the recording paper. Therefore, in order to so hold the recording paper while it is conveyed, a vacuum platen is used to pull the recording paper to the platen surface by means of air suction while the recording paper is conveyed by paper feed rollers. A vacuum platen has numerous suction holes for pulling the recording paper to the platen surface of a box-shaped platen unit. Negative pressure is produced inside the printer by discharging air from the inside to the outside by means of a fan, thereby pulling and holding the recording paper to the platen surface.
Japanese Unexamined Patent Appl. Pub. JP-A-2005-138305 is directed to a printer that has a vacuum platen of which the surface is divided into a grid by a plurality of spaced parallel ribs extending in the recording paper transportation direction on the platen surface, and dividers that divide the spaces between the ribs perpendicularly to the recording paper transportation direction. In such an arrangement, one suction hole is disposed in the bottom of each well surrounded by the ribs and dividers, and when the recording paper is conveyed to a position covering each well, each well becomes a closed space to which suction is applied through the suction hole. A drop in vacuum pressure caused by air leakage from the suction holes when the recording paper does not cover the entire platen surface is thereby suppressed, and a drop in print quality is suppressed.
As is known, if vacuum air flow increases due to air leakage from one or more of the suction holes, the vacuum pressure decreases. In order to appropriately hold the recording paper to the platen surface, the air flow including air leakage must be set and the vacuum platen must be designed to achieve a desirable vacuum pressure within a suitable pressure range.
With the arrangement of JP-A-2005-138305, a closed space is formed around each suction hole covered by the recording paper as a result of dividing the platen surface into numerous suction chambers by means of ribs and dividers. This configuration suppresses air leakage when the recording paper does not cover the entire area of the platen surface, and suppresses an increase in air flow and a drop in vacuum pressure.
However, with the configuration of JP-A-2005-138305 that renders numerous suction chambers and suction holes evenly distributed over the platen surface, many suction holes are outside the width of the recording paper and open to the air when printing on recording paper having a small width. As a result, air leakage from the suction holes on both sides of the paper width is great even after the leading end of the recording paper reaches a position near the downstream end (front end) of the vacuum platen in the transportation direction, and, as a result, the vacuum pressure may be outside the suitable pressure range Pa.
In this situation it is conceivable to adjust the vacuum pressure to within a range suitable for the recording paper by adjusting the suction force of the vacuum fan according to the width of the recording paper and the position reached by the leading end of the recording paper. Alternatively, if the platen surface is divided into a plurality of areas and suction can be applied independently to each area, suction can be applied to only the necessary areas according to the width of the recording paper and the position to which it has been conveyed, and the vacuum pressure can be adjusted to within the suitable range. However, applying such adjustment control and providing such an adjustment mechanism makes vacuum control more complex, or results in a more complex vacuum mechanism and increased parts cost.